1. Field of the Invention
This invention relates to a process for producing unsaturated aldehydes, or unsaturated fatty acids by catalytic oxidation of t-butyl alcohol, or unsaturated hydrocarbons containing 3 to 4 carbon atoms.
2. Description of the Prior Art
Heretofore, various processes have been known for the catalytic oxidation of propylene or isobutylene to the corresponding unsaturated aldehydes. For example Japanese Patent Publication No. 32049/72 discloses the oxidation of olefins over a catalyst comprising molybdenum, antimony, bismuth, iron, nickel and oxygen and a catalyst formed by the addition of tin to the basic catalyst. When propylene is catalytically oxidized with this catalyst, as much as 90 to 91% total selectivity of acrolein and acrylic acid can be obtained at propylene conversions of 95%. However, the amount of the by-products produced is comparatively large, namely, the total selectivity of carbon monoxide and carbon dioxide is as much as 6 to 8%. On the other hand, when isobutylene is oxidized over this catalyst, carbon monoxide and carbon dioxide by-products are produced in such significantly increased amounts that selectivity of methacrolein is decreased from an industrial standpoint, such favorable resuls as improvement in productivity and the removal of the heat of reaction are achieved by suppressing the formation of the gaseous by-products as much as possible. A process in which methacrolein is produced by the gas phase oxidation of t-butyl alcohol is disclosed by laid open Japanese Pat. No. 32814/73. The catalyst used in this process contains thallium, but the yield of methacrolein in a catalyst system not containing thallium is only about 40%.
Another prior art catalytic oxidation procedure is known as shown by Grasselli et al U.S. Pat. No. 3,642,930 in which an oxide catalyst containing molybdenum, iron, bismuth and an alkali metal is employed for the oxidative dehydrogenation of olefins to diene materials. In this type of reaction two hydrogen atoms are withdrawn from the olefin introducing a new site of unsaturation in the olefin. This is a completely different type of reaction, however, than the oxidative reaction of the present invention in which at least two of the hydrogen atoms on a methyl group in an olefin are extracted and replaced by at least on oxygen atom to form at least an aldehyde. If the oxidation reaction proceeds further, the correspondng carboxylic acid is produced. In fact, the Grasselli reference specifically indicates an awareness of the sensitivity of olefins to catalytic oxidation reactions by stating that even within the confines of a specific olefin oxydehydrogenation reaction, one catalyst may quite conspicuously not be able to perform as well as another even somewhat similar catalyst. An example of this unpredictability of olefin oxidation reactions is evident from the fact that while the bismuth, molybolenum, iron and nickel oxide catalyst of U.S. Pat. No. 3,424,631 is particularly effective as an oxydehydrogenation catalyst for the conversion of butene to butadiene, it is significantly less effective for the conversion of isoamylenes to isoprene. Accordingly, a need continues to exist for a method of catalytically oxidizing a C.sub.3 or C.sub.4 olefin or t-butylalcohol starting material to the corresponding unsaturated aldehyde or carboxylic acid in high yields and selectivity.